This invention relates to a method and apparatus for remote metering particularly suited for metering electrical energy.
Because of the drastic increase in energy costs in the past ten years, it has become increasingly more desirable to make efficient use of available energy and the plant that is used to produce it. Individual accountability for energy consumption has proven to be a powerful incentive to energy conservation, leading to increasing demands for individual metering of the energy consumption of each individual entity where some form of master metering might previously have been used. Thus, instead of accepting a percentage share of the electric bill derived from a master meter in an office building or condominium, tenants are increasingly demanding individual metering of their own electrical energy usage. Individual metering rewards those tenants who practice conservation by allocating to them only their actual energy costs. It is advantageous to the landlord because it transfers to the tenant resonsibility for costs that tend to rise faster than the rent and over which the landlord has no control. Perhaps most important, to the electric utility and the community, individual metering means more efficient use of existing generating capacity and therefore at least some respite in the struggle over where to locate and how to finance additional capacity.
While there are substantial incentives for individual metering, the conventional electromechanical meters are not an adequate solution. These devices must be read manually, requiring a large labor force and imposing a difficult problem in where to locate them. As will be appreciated, the location problem is particularly acute when individual meters are to be retrofitted in a building that was formerly master metered. Electromechanical meters also have several inherent problems. They are not very accurate, typically being designed for accuracies of +0.5% under ideal conditions and +2% of a specified range; they slow down with age and at low currents produce low readings; they are position and magnetic field sensitive; and their accuracy in monitoring electrical energy consumption by some modern appliances or under transient conditions may be very poor.
Another shortcoming of conventional electromechanical meters is their inability to provide at reasonable expense time-of-day metering so that power companies could charge for power as a function of load factors. Such capability has become increasingly more desirable as a means of distributing load and therefore diminishing the need for more generating capacity.
Numerous techniques have been devised for remote metering. See, for example, U.S. Pat. Nos. 3,153,780, 3,747,068, 3,818,481, 4,004,097, 4,139,735, 4,161,720 and 4,239,940. While numerous techniques have been devised, there are many problems with them. Some techniques require the use of separate communication lines for the meters, while those which use current carrier systems are subject to severe noise problems. Few, if any, take full advantage of the size reductions, accuracy and economy available from digital computer circuitry.